Some others, like Mozart's Twelve Variations on "Ah vous dirai-je, Maman" and Tchaikovsky's Rose Adagio from The Sleeping Beauty, can be found on the Twinkle Little Star album.
Masaru Yokoyama's arrangement of Chopin's Ballade No. 1 in G minor can be found on Yuna Shinohara's Estreno album.
The version of wacci's Kirameki that is played in the final episode can be found on the limited edition Kirameki album.
The Boku to Kimi to no Ongakuchou album contains the vast majority of the performances you're looking for.
Some others, like Mozart's Twelve Variations on "Ah vous dirai-je, Maman" and Tchaikovsky's Rose Adagio from The Sleeping Beauty, can be found on the Twinkle Little Star album.
Masaru Yokoyama's arrangement of Chopin's Ballade No. 1 in G minor can be found on Yuna Shinohara's Estreno album.
The version of wacci's Kirameki that is played in the final episode can be found on the limited edition Kirameki album.